1. Field of the Invention
The present invention relates to an optometric apparatus, an optometric method, and an optometric server for performing eye examinations to determine the refractive power of eyeglasses or contact lenses. More particularly, the invention relates to an optometric apparatus, an optometric method, and an optometric server for performing subjective eye examinations using a computer screen.
2. Description of the Related Art
Conventionally, a subject must go to an ophthalmologist or to an eyeglass shop to have their visual acuity examined subjectively or objectively by following examiner's instructions. Generally, to perform an objective eye examination, the examiner measures objectively the refractive coefficient of a subject's eye using an auto-refractometer and then lets the subject wear a ready-made corrective lens to check the resulting subject's visual acuity. On the other hand, to perform a subjective eye examination, using a vision test table which indicates symbols such as Landoldt rings as shown in FIG. 19, the examiner points to a symbol or character on the vision test table to determine how the symbol or the character is viewed by the subject, thereby determining the subject's visual acuity based on the subject's response.
Recently, a quantum leap has been made in ordinary household environments by the Internet. As a result, this permits consumers to check their visual acuity at home and purchase eyeglasses or contact lenses without having to go to an ophthalmologist or to an eyeglass shop.
As a matter of fact, when the consumers measure their visual acuity at home, they cannot conduct the objective eye examination because they have no test apparatus such as the auto-refractometer at home. Thus, to make measurements of visual acuity via a network such as the Internet, it is necessary to send image data to display the vision test table as shown in FIG. 19 on the screen of a subject's computer, thereby allowing the subject to determine the smallest target whose features can be visually identified by the subject.
However, generally available vision test tables are configured to display many slightly different size targets on a single screen. This configuration prevents the subject from easily making a proper determination of which target was the smallest one that could be visually clearly identified by the subject. Consequently, the subject sometimes indicated a preference for a target other than the smallest one that could be visually recognized by the subject, which results in an erroneous vision test result. Additionally, the vision test alone is not sufficient for a subject with astigmatism. Thus, an astigmatic dial as shown in FIG. 20 is conceivably presented on the computer screen to elicit from the subject a response as to the orientation in which the subject can clearly identify the dial. However, the astigmatic axis may vary depending on the distance between the subject and the computer screen, causing a simple determination of whether the orientation can be clearly identified to possibly lead to an improper determination of the astigmatic axis.
During a visual acuity measurement performed in the presence of an examiner, even a wrong response made by the subject as to his preference of targets could be checked by knowing the course of the response. However, in the absence of the examiner, it is impossible for a third party to determine whether the preference indicated by the subject is a proper or improper one.